diff --git a/src/numpydantic/interface/interface.py b/src/numpydantic/interface/interface.py
index fd14931..3dfddaf 100644
--- a/src/numpydantic/interface/interface.py
+++ b/src/numpydantic/interface/interface.py
@@ -139,7 +139,7 @@ class Interface(ABC, Generic[T]):
         """Input types for all enabled interfaces"""
         in_types = []
         for iface in cls.interfaces():
-            if isinstance(iface.input_types, Union[tuple, list]):
+            if isinstance(iface.input_types, (tuple, list)):
                 in_types.extend(iface.input_types)
             else:  # pragma: no cover
                 in_types.append(iface.input_types)